The present invention relates to a discharge display system, and more particularly, to a driving circuit for an external electrode type plasma display panel.
Regarding the above-described type of plasma display panels (hereinafter called simply "display panles"), there has been generally known a system in which a row electrode group consisting of a plurality of generally transparent row electrodes arranged in parallel to each other and a column electrode group consisting of a plurality of generally opaque column electrodes arranged in parallel to each other are arrayed in a matrix form, with an ionizable gas interposed between the respective electrode groups, and a discharge luminescent display is made at a crosspoint between a selected row electrode and a selected column electrode. With the aforementioned display panel, an optical image corresponding to an input signal can be displayed by controlling the electrode selecting system for the row electrode and column electrodes in response to the input signal. For instance, an optical image corresponding to an input signal can be displayed on the display panel by successively selecting and scanning the respective electrodes in either one of the row electrode group and the column electrode group, for example, in the column electrode group on a time-division basis, and selectively controlling the respective electrodes in the other electrode group, for example, the row electrode group in response to the input signal while synchronizing with the scanning. In the so-called external electrode type display panel in which the respective electrodes are covered by a dielectric film, it is necessary to drive the panel with an AC voltage, and high frequency pulses called "toggle pulses" are included in the driving signals applied to the row electrode group and the column electrode group. Examples of such a driving circuit are disclosed in "NEC RESEARCH & DEVELOPMENT" No. 30, July 1973, pp 56-63, and in the article by the inventors of this invention presented in "NEC RESEARCH & DEVELOPMENT" No. 46, July 1977, pp. 18-23, especially in FIG. 5 on page 22.
In the case where the external electrode type display panel is operated after it has been left unused for a long period of time, e.g., several days, an initial discharge hardly occurs because the gas in the display panel is almost not ionized, so that it takes a long time until commencement of discharge after application of a firing signal, and thus the display panel has a disadvantage that the so-called turn-on time becomes long.
Also it has a disadvantage that where an unselected cross-point in the display panel newly takes a selected state, likewise the turn-on time becomes long.
A method for improving the delay of the initial discharge is proposed in U.S. Pat. No. 3,842,314 assigned to the same asignee as this application. More particularly, according to this U.S. patent, a circuit for superposing a DC voltage on a driving voltage is added, and thereby only when the power source is switched ON in the first place, all the cells emit light only once. In the subsequent operation, however, the superposed DC voltage has no function to accelerate the firing, so that the reliability of firing when an unselected cell has been newly selected is not high. Furthermore, addition of the above-described DC voltage superposing circuit to every display cell is of high cost and not practical.